In the brass instrument family, the radiated sound can be modified or attenuated using a mute, which is usually inserted in the bell of the instrument. However, this mute cannot control the directivity of the instrument. It could be interesting to develop an active mute which focuses the sound on the instrument player. The objective of this paper is to study the principle and the technological feasibility of a system of loudspeakers placed in front and around the instrument bell in order to control the directivity of the radiated sound without modifying the playability of the instrument. Assuming that the instrument can be modeled as a monopole source, simulation results show that the directivity can be controlled in the low frequency range using different layers of control sources.